Indirect assessment instruments used during functional behavioral assessment, such as rating scales, interviews, and self-report instruments, represent the least intrusive techniques for acquiring information about the function of problem behavior. This article provides criteria for examining the measurement properties of these instruments designed to identify functional relations and reviews 46 studies examining the use and interpretation of the Motivation Assessment Scale (Durand & Crimmins, 1992) or the Functional Assessment Interview (O?Neill et al., 1997). Results indicate at least three inadequacies in the research: (a) insufficient attention paid to evidence based on instrument content and informant response processes, (b) minimal evidence indicating consumer satisfaction and the singular or unique effects of instrument data on intervention development, and (c) excessive emphasis on research designs and measurement properties that assume stability in behavior?environment interactions across contexts.